1. Field of the Invention
This invention relates to a planar wave transducer assembly having particular application for use with a musical instrument (e.g. a piano) for converting planar waves traveling along the soundboard (but not unwanted vibrations which produce sound pressure waves in the air) into an electrical signal that is a very accurate representation of the complex tones of the instrument.
2. Background Art
In my U.S. patent application Ser. No. 07/720,406 filed Jun. 25, 1991, a highly reliable planar wave transducer assembly was disclosed including a pair of foot pads affixed to a planar surface (e.g. the soundboard of a musical instrument), an upstanding leg coextensive to each foot pad and a span bar extending between the legs above the foot pads. A piezoelectric transducer element is bonded to the span bar, and a coaxial cable is attached to the transducer element for connection to an electronic system (e.g. a preamplifier), such that a mechanical bending force applied to the span bar is converted by the transducer element into an electrical signal which is an accurate representation of the complex tones of the instrument. In particular, one of the upstanding legs of the transducer assembly moves with its respective foot pad along the soundboard (at a molecular level) relative to the other leg in response to planar wave energy generated in the soundboard. In this regard, the piezoelectric transducer element is subjected to a warping or bending in response to a corresponding bending of the span bar to which the transducer element is bonded. The ability to detect the movement of one leg relative to the other enables my earlier transducer assembly to be responsive to planar waves that propagate along the surface of the soundboard while being substantially non-responsive to undesirable vibrations that propagate at a right angle to the soundboard. By virtue of the foregoing, my earlier transducer assembly is advantageously adapted to reproduce musical sounds while avoiding the vibration and interference that are typically associated with amplification, such as by microphones, and the like.
It has now been found that the transducer assembly described above works particularly well in musical instruments having relatively thin soundboards including, but not limited to, harps and harpsichords. My new transducer assembly to be disclosed below has been found to be ideally suited for musical instruments having thicker soundboards, such as a piano. To accomplish the foregoing, and as will soon be described, the piezoelectric transducer element of my new transducer assembly is responsive to horizontal compression forces generated by the opposing legs of the assembly rather than to bending forces applied to the span bar as one leg moves relative to the other.